The present invention relates to a bone fixation device for use in maintaining a surgical reference frame. More particularly, it relates to a minimally invasive bone post apparatus for maintaining a dynamic reference frame relative to a patient as part of a stereotactic system, and related method of use.
Stereotactic surgical systems provide surgeons with visual guidance information relating to surgical instruments/probes relative to an enclosed anatomical position, especially within the head or cranium. Basically, a stereotactic surgical system provides a quantitative determination of an anatomical position based upon a scanned image, such as a CAT scan, MRI scan, PET scan, etc. The scanned information is processed by a computer to produce a displayable image of the head. Subsequently, during a surgical procedure, the stereotactic system relates a position of a surgical instrument otherwise deployed within the anatomical body of interest (e.g., the head) relative to the previously-generated scanned information in visual form.
Stereotactic devices are highly useful in the field of neurosurgery as well as other fields, and more recently ENT procedures requiring instrument deployment in close proximity to the optic nerve, carotid artery, skull base, facial nerve, internal auditory canal, etc. A more recent stereotactic system is optical or camera based in which two cameras are employed to visualize a surgical field, digitize the viewed information from the cameras, and relate it via computer graphics to image data generated by the above-described image scanning techniques. The relationship of the optical cameras view and the image data will then make quantitative the anatomy seen in the camera view and also make quantitative the position of surgical instruments such as probes, microscopes, or space pointers, etc. relative to the anatomy via registration of the camera view to the image data. An example such a tandem optical, stereotactic device is available under the trade name LandmarX™ ENT Image Guidance System, from Medtronic-Xomed of Jacksonville, Fla.
Regardless of the exact stereotactic system configuration, a stereotactic or dynamic reference frame must be fixed to the patient's anatomy to provide accurate positioning information. For example, with surgical procedures at or near the patient's head, the reference frame must be affixed to the patient's head via an auxiliary device. To this end, skull posts are commonly employed to rigidly affix the reference frame to the cranium. In general terms, available skull post designs employ one or more bone screws embedded through a relatively large incision into the cranium. In this regard, important constraints relating to the skull post design include precise positioning of the reference frame relative to the patient's head, relatively long-term fixation, and allowing for movement of the patient's head without deviation of a position of the reference frame relative to the head during the surgical procedure. To satisfy these concerns, available skull post designs incorporate a number of additional screws or pins connected to the main post that are otherwise forced through corresponding holes formed in the skull. Thus, the surgeon is required to make a series of accurately positioned incisions and holes prior to mounting of the skull post. While viable, available skull post designs are therefore highly invasive, and cannot readily accommodate for varying contours of a particular patient's head. Further, the reference frame is typically permanently secured to the skull post such that the entire assembly must be removed following patient registration for subsequent sterilization, and then re-secured to the head. Obviously, any deviation in a position of the skull post (and thus the reference frame) prior to a following sterilization may give rise to localization errors. This same concern will arise with stereotactic procedures performed at other anatomical locations where a bone post is used to affix the reference frame relative to the patient.
Surgical stereotactic systems continue to rapidly evolve with improvements to imaging and display components. However, the currently available skull post (or other bone post) design has essentially remained unchanged, and is unacceptably invasive and may give rise to inaccuracies due to subsequent movement between the reference frame and the patient. Therefore, a need exists for an improved surgical reference frame fixation apparatus.